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  Line color based on +/- zero?
Posted by Steve on Sep-10-2021 02:38
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I have a line chart that plots positive and negative values over time. Is there some way to color the line based on whether values are positive or negative?

I saw the example for a multi-color line chart https://www.advsofteng.com/doc/cdperl.htm#multicolorline.htm But that seems to assign colors to line segments.  That's not exactly what I want because a given segment might cross from + to - or vice versa.

  Re: Line color based on +/- zero?
Posted by Peter Kwan on Sep-11-2021 03:03
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Hi Steve,

You can use a y-zone color as the line color:

$myLineColor = $c->yZoneColor(0, 0xff0000, 0x00cc00);
$c->addLineLayer($myData, $myLineColor);

See:

https://www.advsofteng.com/doc/cdperl.htm#XYChart.yZoneColor.htm

Regards
Peter Kwan

  Re: Line color based on +/- zero?
Posted by Steve on Jan-10-2022 03:24
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So how do I do this for a secondary axis?  I've tried the below, but it doesn't work:

$c = new XYChart(800, 480);
$c->setPlotArea(50, 20, 700, 350);
$c->addTitle("New Cases & New COVID-19 Beds 7-Day Avg", "Arial Bold", 10);
$tb = $c->xAxis()->setLabels($labels);
$tb->setFontAngle(90);
$tb->setFontSize(8);
$c->yAxis()->setTitle("New Cases");
$c->yAxis()->setColors($black, $black, $black);
$c->yAxis2()->setTitle("New Beds");
my $a2 = $c->yAxis2()->setColors($black, $black, $black);
$c->addLineLayer($data0, $black);
#$c->addLineLayer($data0, 0x0000c0)->setLineWidth(2);
my $myLineColor = $a2->yZoneColor(0, $green, $red);
$l2 = $c->addLineLayer($data2, $myLineColor)->setUseYAxis2();
$c->makeChart("casevbeds.png");

  Re: Line color based on +/- zero?
Posted by Peter Kwan on Jan-10-2022 12:35
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Hi Steve,

The issue is in the line:

my $a2 = $c->yAxis2()->setColors($black, $black, $black);

The Axis object is the returned value of yAxis2, not setColors. You can modify it to:

my $a2 = $c->yAxis2();
$a2->setColors($black, $black, $black);

Regards
Peter Kwan

  Re: Line color based on +/- zero?
Posted by Steve on Jan-10-2022 23:13
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When I change code to

my $a2 = $c->yAxis2();
$a2->setColors(0x000000, 0x000000, 0x000000);
$c->addLineLayer($data0, $black);
my $myLineColor = $a2->yZoneColor(0, $green, $red);

I get an error on the last line:

unknown method Axis.yZoneColor

  Re: Line color based on +/- zero?
Posted by Peter Kwan on Jan-11-2022 00:59
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Hi Steve,

Sorry, the yZoneColor line should be:

my $myLineColor = $c->yZoneColor(0, $green, $red, $a2);

Regards
Peter Kwan